I am working on a hobby project, which includes a small graphics lcd, 3AAA battery holder, an opamp, and a micro. I'm at the point where I will mount the breadboards in a box, and decided I didn't want a normal on/off switch because of several reasons- I don't like on/off switches, I don't like more holes in the box than needed, and I hate finding the power was left on accidentally. For various reasons, I also don't want to use any low power sleep mode and just want to power everything off by keeping power from the 3.3v regulator (MCP1700). Current draw when on is <20ma.
So, I want to power up the device with a single push button switch, and also use that switch as the only user input switch (to cycle between pages viewed on the lcd). The device will power off by inactivity timeout. 1 switch, no thought required to operate it- just keep pushing the only switch in sight.
What I came up with is the circuit below, from parts I already had, and trying to get as minimal as possible. It seems to get enough current with the 4.7k resistor to get to a point where the micro can turn on Q2 (10k works mostly, but not 100%, so I dropped it down to 4.7k).
Is there a simpler/better way to do this? (with simple/common components). I'm on shaky ground using the power via R1 into an i/o pin to jump start the micro. I have been playing with it for a few days, and it continues to work reliably, though. Also, what is a good way to measure low current? I can check the voltage drop at R1 when off, which is ~1mv (decent Fluke meter), so I calculate about ~200nA (if actually 2mv, ~400na). If that is actually the case, then I think that is plenty good for the batteries being used.
Thanks for any better ideas.